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1. Field of the Invention
The present invention involves the simultaneous measurement of light scattering from multiple, independent samples, comprising solutions containing polymers and/or colloids.
2. General Background of the Invention
The following patents are incorporated herein by reference:
U.S. Pat. Nos.: 3,809,912; 4,541,719; 5,011,286; 5,185,641; 5,255,072; 5,427,920; 5,907,399; 6,118,531; and 6,118,532.
U.S. Pat. No. 5,427,920 discloses multiple fluid compartments, each with its own light source and light detector.
U.S. Pat. No. 5,011,286 discloses a multisensor particle counter using a single beam to measure several fluid sample portions simultaneously.
U.S. Pat. No. 5,255,072 discloses using a single sensor to measure several fluids simultaneously.
The present invention comprises Simultaneous Multi-Sample Light Scattering, or SMSLS, for absolute and relative characterization of dilute macromolecular/colloidal solutions. Dilute here means that for a light beam incident on the solution the majority of scattering events are single scattering events. (Herein, xe2x80x98single scatteringxe2x80x99 will refer to the case of light scattering in a solution wherein the majority of detected, scattered photons have scattered only once.) In prior art, light scattering devices have been made to measure only one sample at a time. This is in large part due to the fact that great care and expense has been taken to produce high quality optical cells for single samples, and it has not been obvious to practitioners that multiple independent measurements might be economically or technically feasible. Current art has also not taken account of the fact that significant advantages exist for being able to simultaneously measure the light scattered from multiple, independent samples. For convenience, the invention will be referred to herein as Simultaneous Multi-Sample Light Scattering, or SMSLS.
Emerging needs in new fields of polymer/colloid science and application now make such a multi-sampling capability extremely desirable. The following is a non-exhaustive list of fields in which multi-sampling will be of great utility:
1) Light scattering art has reached the phase where processes occurring in polymer/colloid solutions can be followed online.1 At the industrial level, where large reactors are to be monitored, there is often considerable inhomogeneity within the reactor, so that samples withdrawn from different locations in the reactor can have different characteristics. Continuous and multi-stage reactors are other examples where SMSLS may be advantageous. The SMSLS invention will allow multiple samples withdrawn from different reactor locations to be characterized simultaneously, with a single device and computer. In prior art, the expense involved in using multiple, single sample instruments, each requiring a separate computer, with the attendant complication of trying to integrate all their signals, makes such multi-sampling economically and technically unattractive.
xe2x80x98Computerxe2x80x99 used throughout the description of this invention refers to any device capable of receiving signals from light detectors, and performing the required data reduction and analysis on these signals. Hence, xe2x80x98computerxe2x80x99 can refer to any commercially available computer (e.g. such as those sold by IBM, Dell, Apple, etc.), including workstations (e.g. Sun Microsystems), as well as any microprocessor-based device whether commercially available or designed specifically for the data acquisition and analysis functions described herein.
2) In the emerging field of combinatorial chemistry applied to new polymer synthesis, research and development is focused on running dozens of reactions (xe2x80x98reactionxe2x80x99 as used herein refers to both chemical reactions involving the making and breaking of covalent bonds, as well as any reaction that a polymer or colloid can have in response to time, interactions with itself or other agents, etc. that do not involve making or breaking covalent bonds; such reactions can include aggregations of polymers, changes in dimensions, hydrodynamic properties, excluded volume interactions, etc.) in parallel in microliter quantities. No light scattering technology currently exists which can make simultaneous, multiple measurements. In its simplest version, SMSLS will be useful in providing immediate information on whether polymer reactions are occurring at all, and what the relative rate constants are for each sample. In the more refined version, where absolute calibration would be made and exact sample concentration known or measured, the device would give absolute molecular weight characterization in real-time of the polymers as they polymerize. Again, such analyses can be made with a single device and a single computer. The analyses might be carried out on samples flowing through the SMSLS device, pipetted into and at rest in the SMSLS device, or samples in cuvettes which can be inserted into the SMSLS device. Hence, the SMSLS invention is expected to have favorable implications for this emerging field, which is being pursued by academic scientists, multi-national corporations, and small, emerging companies.
3) In university, pharmaceutical, industrial and other laboratories, time-dependent processes can be followed, using SMSLS, on many independent samples of varying composition, in order to determine the evolution and stability of solutions; e.g. determination of the shelf-life of a pharmaceutical product, the stability of an organic polymer in different solvents, the enzymatic degradation rates for polymers, or the interaction of small molecules with larger ones, etc. Users can have direct, real-time, graphical and numerical representations on their computer screens of the simultaneous evolution of many samples. Under current art, such measurements require monopolizing an expensive light scattering device and computer for each sample being tested. With an SMSLS device with, say, 250 sub-chambers (xe2x80x98Sub-chamberxe2x80x99 as used herein refers to any sort of receptacle which can receive a liquid sample, and has means for introducing light to be scattered, and a means for detecting the scattered light. The sample can be introduced into the chamber by any means, such as flow, pipetting, being held in a separate sample cell which is inserted into the sub-chamber, etc.), all monitored by a single computer, measurements that might take a year of monitoring might be performed in a single day.
4) In Size Exclusion Chromatography (SEC) applications, and other separation/fractionation analyses, the SMSLS invention can be used as a detector for multiple SEC or other separation/fractionation devices. Currently, a costly light scattering detector is needed for each separation device. With this invention only a single SMSLS device would be needed for multiple separation devices. In this case, a separate computer would most likely be used to analyze the detected light from each sub-chamber, since, normally, there is a dedicated computer for each SEC instrument and the other detectors associated with each (e.g. refractive index detector, viscometric detector, ultraviolet/visible detector, etc.).
5) In a setting where high sample characterization throughput of unfractionated polymer batches is desired, the SMSLS invention could be readily adapted to robotic automation, wherein the samples could be automatically and simultaneously prepared, then simultaneously measured by SMSLS.
In summary SMSLS can be of decisive utility in academic and industrial laboratories that deal with, but are not limited to, polymers, resins, adhesives, foodstuffs, pharmaceuticals, water purification agents, pulp, paper and fiber products, coatings, etc.
The present invention involves making a single device with multiple sub-chambers, each of which is equipped with its own independent scattered light detection means (e.g. one or more optical fibers, window(s), etc.). Each sub-chamber can hold an independent liquid sample, and light is incident on each sub-chamber. The scattered light from each sample will be detected by the detection means in each sub-chamber. Each detection means is coupled to its own light sensitive detector (e.g. a photodiode or charge coupled device), the output of which is led into a computer for analysis. Hence, the device permits multiple, independent samples to be measured simultaneously and analyzed by a single computer.
A technical clarification of the meaning xe2x80x98simultaneousxe2x80x99 in the context of SMSLS is in order. In general the analog or digitized voltage values of the photodetectors for each sub-chamber are read sequentially, so that, technically, one sub-chamber value might be read microseconds, milliseconds or seconds before the next one. In this case, xe2x80x98simultaneousxe2x80x99 means that the values from all the individual sub-chambers, or a subset of the sub-chambers, are read (and recorded and/or processed), before another round of data is collected for some or all of the sub-chambers, even when the sub-chamber voltages are read sequentially during a given data collection round. This definition also applies to the case where multiple sequential readings of all sub-chambers are made during a given round in order to average the signal from each chamber.
The sub-chambers can be fabricated all with the same volume, or different volumes can be assigned to the fabrication of individual sub-chambers or groups of sub-chambers. Sub-chambers can be designed and fabricated with a wide variety of volumes. In micro-chemical applications, the sub-chambers will typically have volumes of from 5 microliters to 200 microliters. In situations where sample volume is less critical, sub-chambers can typically have volumes from 200 microliters to 2 milliliters. There may be some contexts, particularly in industrial settings where huge reactor volumes are used (e.g. 1000 gallon reactors), and so small sub-chamber volume is not a critical issue. In such cases sub-chambers may typically hold volumes from 2 milliliters to over 20 milliliters.
The device only needs to have a single incident source of light (e.g. a laser) that irradiates the main chamber containing all of the sub-chambers, although multiple light sources can also be used, as detailed below. This can be achieved in series-mode, or parallel-mode:
In the series-mode, the incident light is collimated and sent through a line of sub-chambers, in series, each separated by a transparent window. There can be more than one light source and sets of sub-chambers.
In the parallel-mode, the light can be split at its output so that each sub-chamber receives its own, independent portion of the incident light, in parallel. Alternatively, each sub-chamber or set of sub-chambers can have its own unsplit light source.
One advantage of the series-mode is that little power is lost from sub-chamber to sub-chamber, and only one light source is needed per line of sub-chambers. The disadvantage is that if a window(s) between sub-chambers fouls (e.g. from a xe2x80x98dirtyxe2x80x99 sample), or a sample in a sub-chamber becomes turbid, then all the sub-chambers down-beam will be affected. Series-mode is expected to be of greatest utility when the samples remain transparent and don""t become cloudy in time, or otherwise undergo large changes in light transmittance.
In the parallel-mode, there is no problem if any one sub-chamber fouls, but there will be an additional cost due to the beam splitting and/or additional light sources. This mode will be especially valuable when the stability and/or evolution of polymer and/or colloid samples leads to significant turbidity in the samples.
In either series- or parallel-modes, each sub-chamber can be independently filled with sample solutions. This can occur in a number of ways: i) the samples can be introduced into sub-chambers via a pumped flow, ii) they can be pipetted, or otherwise manually or robotically transferred into the sub-chambers, or iii) each sub-chamber can contain its own miniature receptacle for inserting a cell.
In its simplest form, the light scattering can give immediate information about relative polymer and/or colloid size, stability and evolution of samples, and show whether a polymerization reaction is occurring or not. In its more refined version it will allow the absolute mass of polymers and/or colloids, and their dimensions to be determined. It is possible that other spectroscopic devices could be incorporated in the invention, such as dynamic light scattering, ultra-violet absorption, and refractive index. A viscosity detector might also be incorporated when flow is present.
In principle, dozens, hundreds or more such sub-chambers can be incorporated into the device of the preferred embodiment of the present invention. The sub-chambers can be individually stacked together to provide the user with exactly the number needed, or the device can be manufactured with a fixed number of sub-chambers, and the user just utilizes the number necessary. It is also possible to use multiple light sources (e.g. lasers), wherein each light source irradiates a chamber with one or more sub-chambers. In this case, all the data would still be processed simultaneously by a single computer, except in special cases where multiple computers might be desirable (e.g. when output streams from several independent fractionation devices flow through sub-chambers in the device),
The cost of the chambers should be quite low, because they can be fabricated out of plastics, such as Delrin, blackened metals, or glass. The separating windows in series mode can be inexpensive borosilicates, such as high quality microscope cover slips, which cost only pennies apiece. Flow fittings, which would be optional, can be made from conventional HPLC plumbing or other commercially available or custom built materials. The optical fibers are also inexpensive. Light sources are also inexpensive; e.g. a diode laser with collimation optics, a diode laser without special optics, integral arrays or banks of diode lasers, light emitting diodes, incandescent, gas or arc lights. Likewise, photodiodes, photomultipliers or other detector types (e.g. diode arrays, charge-coupled devices, etc.) are relatively inexpensive.
It is stressed that individual sub-chambers do not need to be in physical contact with each other (e.g. as shown in FIGS. 4, 8 and 9), especially in parallel-mode, where there is not necessarily any advantage to them being in contact. In many cases, however, close, regular spatial proximity of the sub-chambers will enhance the ease of robotic or manual testing; e.g. pipette devices with multiple tips at fixed distances are readily available (for example, the Multichannel Pipette from Rainin Instrument Company allows simultaneously filling sample cells or sub-chambers at fixed spatial separation).
The Following is a Necessary and Sufficient Condition for a Light Scattering Device to be Considered an SMSLS Device.
An SMSLS device is one in which there are always two or more sub-chambers capable of making at least two or more simultaneous measurements on independent samples, even if, at any given time, only one sub-chamber is in use. By this definition there is no SMSLS device with a single scattering chamber that can act as a stand alone device.
Indivisibility: An SMSLS device cannot be taken apart into individual single sample stand alone units (i.e. individual units that could be placed in remote locations and function independently) without the introduction of extra materials (e.g., any one or more of the following; mounting plates, enclosures, fiber optics, lenses, light baffles, light sources, detectors, electrical wires, plumbing connections, baseplates, brackets, electronic circuits, etc.), and/or special procedures such as re-alignment, reconnection of optical, plumbing and electrical connections, etc. Computers and identical software copies are excluded from this definition since they might be needed for completely independent operation of each unit.
Non-constitutibility from stand alone units: An SMSLS unit cannot be constituted from two or more stand alone units without the introduction of an additional, indispensable component(s), whether these be electronic, software, hardware, mechanical, plumbing, etc. Specifically this includes multiplexers, signal processors and/or software with SMSLS capability. In the case of software, this includes software that can store data from independent, simultaneous scattering experiments that could later be analyzed by separate software to yield the results of the independent experiments.